I have tried to use Part Design module to create a body/pad directly inside the assembly container and it doesn't work.

So I assume that part container is needed to create geometry with Part Design Module.

You don't need App::Part here. PartDesign has the "Active Body" concept, which is enough in this case. Just create an assembly, create a body, drag the body to the assembly, then you can create subsequent sketch, pad and pocket, which will be automatically added to that body. The following screencast shows two bodies in the assembly, and you can simple double click any one to switch the active body, and subsequent PartDesign features will be added to that body. The screencast also showcase the fact that A3 container can build geometry too, to support multi-body use case.

realthunder you did many things in asm3 that are just amazing but many things (concepts) are IMO also badly mixed up, please let us work together to straighten things up, we did good on sketcher exports and topo-naming

realthunder you did many things in asm3 that are just amazing but many things (concepts) are IMO also badly mixed up, please let us work together to straighten things up, we did good on sketcher exports and topo-naming

Yeah, sure, just lay your thoughts here. But I'd like them to be a bit more specific.

Anyway, you can also use master sketch to place multiple child parts (bodies). For example, see here

Try Assembly3 (latest version 0.9.1) along with my custom build of FreeCAD at here.
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Just a comment, generally speaking to the App::Part replacement and Assembly 3. I'm not an expert, it's just a thought and I humbly accept that what seem to me important might be a wrong understanding of the situation.

I fear that it gets more and more complicated over time. I'm primarilly testing ASM3 FC branch, but in past months was also forced to test the main development release due to specific features and I see, that the virtual scissors are openning. There are new WBs and features building on top of the updated Body and Part concepts of the main branch. Thus, it seems to me, that it is essential to focus on implementing Realthunders' Part & Link concept into the main development branch first and only then it makes sense to further develop ASM3 features itself.

Because ASM3 future depends on which model will stay. We can see it clearly on the example of re-born A2 (A2+). Only one assembly WB will make it in the long run and it comes down all the way to the App::Part concept, which one.

Thus, it seems to me, that it is essential to focus on implementing Realthunders' Part & Link concept into the main development branch first and only then it makes sense to further develop ASM3 features itself

I think that the maintainers of FreeCAD projects are free to merge the LinkStage3 branch. It is just that they don't want.
Realthunder asked to evaluate the possibility of this merge more than 6 moths ago (30 June 2018) and I do not have yet seen any reply from the main the FreeCAD project leaders.

So I do not think that it would be a good idea stopping the development of ASM3 branch to wait for a merge which probably will never happen.
I like the development direction taken in the ASM3 branch and I would like to see it going on:
- The possibility of adding (in an efficient way) more instances of the same part in an assembly.
- The recent improvements on the scketch tool like external geometry used as constructive lines and the better handling of sketch constraints referring to external geometries

In comparison it seems to me that the main branch is stalled and more focused on programming languages (python 3 vs python 2, perfect adherence to C++ best programming style) than the real CAD stuff. With the only exception of ASM2+ where I may see fast and good progresses but still limited from the missing of LinkStage 3 infrastructure.

The Freecad's version that Assembly3 is using is not exporting the .obj and .stl files well. The parts in the exported files are in random positions. Do you have any ideas to pass through this problem? It would be nice if I could save the assembly in a "normal Freecad format" and open it in the normal Freecad version (obviously without the assembly constraints).

I think that the maintainers of FreeCAD projects are free to merge the LinkStage3 branch. It is just that they don't want.
Realthunder asked to evaluate the possibility of this merge more than 6 moths ago (30 June 2018) and I do not have yet seen any reply from the main the FreeCAD project leaders.

So I do not think that it would be a good idea stopping the development of ASM3 branch to wait for a merge which probably will never happen.

I don't think this is the case, just that getting the Python 3 & Qt 5 transition completed is a higher priority and that doing all three things at the same time would exceed our development bandwidth; as soon as 0.18 is released I believe assembly will be the main thrust of 0.19 development.

The Freecad's version that Assembly3 is using is not exporting the .obj and .stl files well. The parts in the exported files are in random positions. Do you have any ideas to pass through this problem?